Holdback devices

ABSTRACT

The specification describes a holdback device for controlling the flow of a web of paper in a high-speed line printer. The device prevents reverse movement of the web, for example when being printed upon, and allows forward movement of it. The backward movement - caused by the web being gripped between the rotating character shaft and the printing hammers - results in the misalignment of printed characters, and may even cause damage to the web. The devices described have a blade or pawl movably mounted in contact with the paper web, and pivotally bearing on a fixed surface. If reverse movement starts to take place the blade or pawl pivots on the fixed surface and grips the web between it and a drum contacting the other side of the web. The drum is free to move only in a sense such as to move the web in the forward direction and it is driven in this sense simultaneously with or immediately prior to movement of the web in the forward direction - when the printing of a line of characters has been completed thus aiding the unlocking of the blade or pawl.

United States Patent Ronald John Frank Eitel Stoke-on-Trent,Staffordshire, England (c/o English Electric Computers, Ltd,

[72] inventor Kidsgrove, England) [21] Appl. No. 731,231 [22] Filed May22, 1968 [45] Patented Mar. 9, 1971 [3 2] Priority May 24, 1967 [3 3]Great Britain [31 24059/67 [54] HOLDBACK DEVICES FOREIGN PATENTS1,022,370 3/1966 GreatBritain Primary Examiner-Ernest T. Wright, Jr.

Assistant ExaminerStephen C. Pellegrino Attorneys-Misegades and Douglas,Keith Misegades and George R. Douglas, Jrl;

printing hammers results in the misalignment of printed characters, andmay even cause damage to the web. The devices described have a blade orpawl movably mounted in contact with the paper web, and pivotallybearing on a fixed surface. If reverse movement starts to take place theblade or pawl pivots on the fixed surface and grips the web between itand a drum contacting the other side of the web. The drum is free tomove only in a sense such as to move the web in the forward directionand it is driven in this sense simultaneously with or immediately priorto movement of the web in the forward direction when the printing of aline of characters has been completed thus aiding the unlocking of theblade or pawl.

HOLDBACK DEVICES This invention relates to holdback devices forcontrolling the flow of a paper web. I

Such devices find application in for example, high-speed line printerswhich print output data from digital data processing equipment.

Holdback devices prevent the reverse movement of the paper web due tothe impulsive forces produced in the web when printing takes place, thepaper web being momentarily gripped between a rotating character shaftand one or more printing hammers.

Alternative types of this device have been proposed. One, that describedin British Pat. No. l,022,370,describes a loose cam one end of whichengages the paper web at a position opposite the printing table. Theother end of the cam bears against a fixed surface. Reverse movement ofthe web causes the cam to rotate against the fixed surface and clamp theweb to the printing table.

The above proposal has a disadvantage which the present invention seeksto overcome, namely the cam having been locked onto the paper web by theaction of printing needs to be unlocked to allow the paper web to bemoved in the forward direction after printing. In earlier arrangementsthe paper traction devices have had to perform the unlocking action, anddamage to the paper web has sometimes resulted.

According to a feature of the invention a holdback device for permittingmovement of a web of paper in a forward direction and preventing reversemovement of the web includes a first member having an operative edge orsurface in contact with one side of the paper web, and a reaction memberhaving a reaction surface in contact with the side of the web oppositethe operative edge or surface, the operative edge or surface beingmovable towards the reaction surface in response to a small reversemovement of the paper web whereby the paper web is gripped between thefirst and reaction members and is thereby prevented from substantialfurther reverse movement, and both the first member and the reactionmember being movable to release the paper web subsequent to suchgripping action so as to allow substantially unimpeded forward movementthereof.

Preferably the movement of the reaction member results in the reactionsurface moving in the forward direction to release the paper web.

Preferably the reaction member is constrained to prevent movement of thereaction surface in the reverse direction.

According to another feature of theinvention a holdback device includesdriving means for driving the reaction member so as to move the reactionsurface in the forward direction.

Preferably the driving means is operable to commence the forwardmovement of the reaction surface a short time before the forwardmovement of the paper web'commences.

According to another feature of the invention a holdback device includesa reaction surface provided by an arcuate peripheral surface of a membermovable about an axis aligned transversely of the paper web.

Preferably the said reaction member is cylindrical, having said axisthrough its center.

According to another feature of the invention the first member comprisesa blade having an operative edge in contact with the paper web andfurther includes holding means, the holding means including a fixedsurface against which the blade pivotally bears, the blade being movablysupported to make an obtuse angle to the forward-direction of motion ofthe paper web so as to effect gripping and releasing of the paper web.

According to another feature of the invention the first member comprisesa pawl having radiused opposed ends, one of which provides the operativesurface and the other of which bears on a fixed surface generallyparallel to the paper web, rocking of the pawl on the fixed surfaceproviding for the gripping and releasing of the paper web.

Two alternative holdback devices according to the invention forincorporation in a high-speed line printer will now be described by wayof example, with reference to the accompanying drawing, in which:

FIG. 1 shows in diagrammatic form a side elevation of the relevant partsof a line printer including one of the paper holdback devices;

FIG. 2 shows a vertical cross section of the holdback device shown inFIG. 1;

FIG. 3 shows a vertical cross section of the second holdback device; and

FIG. 4 shows graphs depicting to the base of time the speed of arotatable drum constituting a part of each of the paper holdback devicesand the associated paper web.

Referring to FIG. 1, the printer has an elongated character shaft 5 ofwhich one end is seen. The shaft 5 carries lines of character types 6which extend along its length, the lines of character types 6 beingspaced circumferentially around the shaft 5. A printing ribbon 7 havinga width as great as the length of the lines of type 6 is hung below thecharacter shaft 5 and arranged to be wound by means not shown betweentwo ribbon reels 7. A fixed platform 8 is mounted beneath the charactershaft 5 and supports a paper web 9 on which printing is to be performed.The paper web 9 is fed from a container 10 by a driven sprocket wheel 11through a paper reservoir device 12, beneath the character shaft 5, pasta holdback device 13, which will be described in detail below, over afurther driven sprocket wheel 14 to a container 15. The platform 8 has acentral gap 16 through which a series of printing hammers 17 may beseparately impulsed to press the paper web 9 against the types 6 on thecharacter shaft 5, the ribbon 7 causing an impression of the charactertypes 6 to be printed on the paper web 9. i

In operation, the paper web 9 is advanced in steps by the sprocketwheels 11 and 14 in the direction of the arrow A. During printing theshaft 5 is rotated continuously in the direction shown by arrow B, andat a given instant a line of particular character types 6 faces theoperating ends of the hammers 17, so that selected hammers may beoperated to print in line on the paper web 9 impressions of theseparticular character types 6.'When the shaft has rotated so as topresent the next line of character types 6 to the paper web 9 selectedother hammers 17 may be operated to print impressions of these furthercharacter types 6 on the paper web 9. This process continues until thecomplete line of characters has been printed. The paper web 9 is thenstepped on in the forward direction by the sprocket wheels 11 and 14,the paper reservoir device 12 permitting high acceleration of the paperweb 9.

When one or more of the hammers 17 are being operated to press the paperweb 9 against the ribbon 7 and into contact with the rotating charactershaft 5 there is a tendency for the paper web 9 to be carried in thereverse direction due to the rotation of the character shaft 5. Suchreverse movement, if not prevented prevents the printing of a straightline of characters on the paper web 9. The holdback device 13 alsoreduces the settling time of the paper web 9 after forward movement ofit. Torsional deflections in the sprocket wheel connecting shafts (notshown) set up oscillations in the paper web 9 along its length. Theholdback device 13 by preventing reverse movement of the web 9 whileallowing forward movement heavily damps these oscillations therebyreducing the time in which the web 9 comes to a rest. Such reversemovement is in fact inhibited by the holdback device 13 which extendsacross the width of the paper web 9 and which will now be described indetail with reference to FIG. 2.

A plurality of blades 23 are supported by pins 22 mounted in a supportbar 21. Set in a rod 24 are springs 25 whose ends contact the blades 23so as to urge the operative edges of the blades 23 into contact with thepaper web 9. Opposite the operative edges of the blades 23 and anopening 27 extends across the width of the platform 8 and through thisopening a rotatable drum 26 having a rough outer surface contacts theunderside of the paper web 9.

The drum 26 is arranged for rotation only in the sense shown by arrow Cso that in operation the paper web 9 is allowed to move freely in theforward direction. However, any movement of the paper web 9 in thereverse direction results in the operative edges of the blades 23applying pressure to the paper web 9. Any further movement in thereverse direction therefore increases greatly the pressure exerted onthe web 9 by the operative edges of the blades 23, substantiallypreventing further movement in the reverse direction.

The rotatable drum 26 is rotated by a motor 28 (FIG. 1), in thedirection of the arrow C shortly before the paper web 9 is to be movedon by the sprocket wheels 11 and 14 after the printing of a line ofcharacters, the rotation of the drum 26 being continued until the paperweb 9 is moving. The rotation of the drum 26 urges the paper. web 9 atthe region in contact with the blades 23 in a forward directionindicated by the arrowA thus over overcoming the tendency of the blades23 to continue pressing onto the paper web 9 and so minimizing theinstantaneous forces acting on the paper web 9 to accelerate it.

The drum 26 may be driven continuously while the paper web9 moves in theforward direction indicated by the arrow A, acting as a further drivemeans for the web 9.

Referring now to FIG. 3 which shows the second holdback device 30, thisdevice includes an upper bar 33, mounted on a lower bar 34 which has ahole 41 passing through it, the upper bar 33 being substantiallyparallel to the paper web 9. The bar 34 is slotted at 39 to accommodatea plurality of spaced pawls 35. Each pawl 35 has radiused ends 36 and 37and is of length greater than the perpendicular distance between theplatform 8 and a lower surface 38 of the bar33. The pawl 35 ispositioned by a tension spring 31 and surface 40 of the bar 34, with theend 36 in contact with the surfaces 38 and 40 and its end 37 resting onthe paper web 9. The tension spring 31 passes through the hole 41 and isattached to a fixed member 32. Opposite the end 37 of the pawl 35 thereextends across the width of platform 8 a gap 27 through which the outersurface of the rotatable drum 26 contacts the paper web 9.

As described above the drum 26 is free to rotate in the forward senseonly so that in operation the paper web may move freely only in theforward direction indicated by the arrow A. However, movement of thepaper web 9 in the reverse direction causes the ends 36 and 37 of thepawl 35 to roll on the surface 38 and the paper web 9 respectively so asto force the pawl towards pawl 35 towards an attitude perpendicular tothe paper web 9. The rough outer surface of the drum 26 prevents thepaper web 9 from slipping back under the end of the pawl 35. Thetendency for the pawl 35 to roll greatly increases the reaction forceexerted on the paper web 9 by the pawl 35 and increases the frictionforce acting on the paper web 9 to such an extent that further reversemovement of the paper web 9 is prevented. The rotatable drum 26 isrotated in the direction of the arrow C shortly before the paper web 9is to be moved on in the forward direction indicated by the arrow A, therotation of the drum 26 continuing until the paper web 9 is moving sothat any tendency for the pawl 35 to continue to press onto the web 9,so causing large forces to act on the paper web 9 during itsacceleration, is overcome. Again the drum 26 may be continuously drivenwhile the paper web 9 is moved.

FIG. 4 shows in a diagrammatic form the relative speeds w and v at whichthe drum 26 is driven and the paper speeds w and v at which the drum 26is driven and the paper web 9 is moved respectively, when the paper web9 is moved on. It will be observed from the upper curve that therotation of the drum 26 starts prior to the acceleration of the web 9 asshown in the lower curve. The time elapsed between the drum 26 startingto rotate and the paper web 9 being moved is adjusted such that it issufficient for acceleration of drum 26 to cause the paper web 9 to befreed from the gripping means, i.e. the blades 23 or the pawls 35 beforeforward movement of the web 9 takes place.

The drum 26 may be free to rotate in the forward sense when not beingdriven in that sense; if such were the case the drum 26 would rotate fora period longer than that shown in the upper curve of FIG. 4, beingcaused to rotate by the paper web 9 as it passes the drum 26.

Though the paper holdback devices as described with reference to FIGS. 2and 3 extend across the full width of the paper web 9 each paperholdback device may consist instead of a pluralityof separate unitsplaced side-by-side across the width of the web 9.

It will be appreciated that other forms of a reaction member, while notas preferable, are possible; and that other types of movement of areaction member may be used, c. g. the reaction member may moveperpendicularly away from the web when forward movement of the webcommences.

It will be appreciated also that while the drum 26 has been described asbeing driven by a motor to release the web 9 this may not necessarily beso; the drum 26 could be freely rotatable, being driven by the paper web9, though this is not as advantag'eous.

Iclaim:

1. Paper-feeding apparatus including a planar bad for supporting a webof paper to be fed; means for feeding the web in one direction along thebed having a gap therein extending transverse to said one direction; aroller having an axis of rotation mounted in the gap with said axisextending parallel to said planar bed and transversely to said onedirection such that a part of the surface of the roller lies in theplane of the bed; a member resiliently mounted relative to said rollersuch that the web may be fed freely between the member and the roller insaid one direction and is gripped between the member and the roller by awedging action acting substantially along a line parallel to said axisof rotation as a result of movement of the web in a second directionopposite to said one direction; means for rotating the roller about itsaxis to move said part of the surface of the roller in said onedirection to facilitate the release of the web from the wedging actionwhen the web is moved in said one direction aftermovement in the seconddirection.

2. Apparatus as claimed in Claim 1 wherein the rotating means isoperative to rotate the roller intermittently, rotation of the rollerbeing initiated immediately prior to feeding the web in said onedirection and continued until the web is moving in said one direction.

1. Paper-feeding apparatus including a planar bad for supporting a webof paper to be fed; means for feeding the web in one direction along thebed having a gap therein extending transverse to said one direction; aroller having an axis of rotation mounted in the gap with said axisextending parallel to said planar bed and transversely to said onedirection such that a part of the surface of the roller lies in theplane of the bed; a member resiliently mounted relative to said rollersuch that the web may be fed freely between the member and the roller insaid one direction and is gripped between the member and the roller by awedging action acting substantially along a line parallel to said axisof rotation as a result of movement of the web in a second directionopposite to said one direction; means for rotating the roller about itsaxis to move said part of the surface of the roller in said onedirection to facilitate the release of the web from the wedging actionwhen the web is moved in said one direction after movement in the seconddirection.
 2. Apparatus as claimed in Claim 1 wherein the rotating meansis operative to rotate the roller intermittently, rotation of the rollerbeing initiated immediately prior to feeding the web in said onedirection and continued until the web is moving in said one direction.